[eluser]Otemu[/eluser]
1. If you commonly use the helper/lib or model throughout your site then autoload it
2. If you commonly use the helper/lib or model in every function of that controller then load it at controller level
3. If it not commonly used in other method/functions then load it at this level
In terms of benchmarking I am not sure how much diff it makes, could be talking milliseconds.